The present invention relates to a method and apparatus for joining electric component pins and electric wires. The invention has great utility in but is not limited to joining insulated magnet wires to multipinned terminal blocks and non-insulated wire strands to multipinned terminals.
The art of joining wires to wires and wires to metal pins is quite old. The art of joining wires to wires to form pigtails or splices includes U.S. Pat. No. 4,687,900 wherein stranded wire 12 is joined to initially insulated magnet wire by placing these wires in the notch of a lower fusing electrode and joining them through the application of pressure, heat, and current through the engagement of the upper fusing electrode. Care is taken to locate the non-insulated stranded wires above and in contact with the insulated magnet wire so that the current path is completed through the wire 12 to the side walls of the lower electrode to generate electrode heat, for burning off the wire 14 insulation and establishing a current and heating path through both wires to be joined. A technical problem associated with this approach results from the wires being unsymmetrically placed or held in the notch. This approach may cause the initial application of fusing current and heat to the insuated wire 14 being unevenly applied to remove or burn off the insulation. This effect would cause non-uniform or unreliable joints from one temination to the next.
Attempts have been made for joining non-insulated wires to pins, however, these attempts experienced reproducability and reliability problems because it was difficult to position the small pin exactly centered on the wire. The pin usually shifted toward one side of the notch or the other causing the initial current to pass more through one notch side wall than the other. This non-symmetrical flow heats the bottom electrode notch and the magnet wire unevenly causing non-uniform results from one termination to the next.
Another technical need in the art relates to the time, costs and inefficiency of setting up to implement the fusing action and the requirement to move or index either the work piece or the upper and lower fusing heads to join a multiplicity of wires to a multiplicity of pins on a single device. Present apparatus require the operator to set up the pin, wire and lower electrode assembly before each fusing operation. This results in a slow, tedious, costly process with high chance of human error that reduces quality and yields from the system.
The exemplary method and apparatus of the present invention avoids the above mentioned problems and provides new quality and production advantages. According to the principles of the invention, the apparatus includes a lower fusing electrode having a notch with side walls converging to a bottom groove. An insulated or uninsulated wire of predetermined gauge is placed at or near the bottom groove. The metal pin is then placed within the notch. The pin and notch are dimensioned and cooperate so that the pin is initially held spaced above the wire by both side walls of the notch. Preferably, the distance between bottom of the pin and top of the wire is predetermined as described below. To accomplish the fusion joint, the upper electrode contacts the top of the pin, and current is applied by the power control unit. Initial current flows through the upper electrode, through the pin thence through the solid portion of the lower electrode beneath the wire to ground. Because the pin has low resistance and the lower and upper fusing electrodes high resistance, the solid electrode portion beneath the wire heats to burn off the wire insulation and heat the wire. Because the notch walls, wire location at the bottom groove, pin, and upper electrode are all easily symmetrically oriented, the flow of current and heat flows are uniform and uniformly heat the pin and wire. Insulation is quickly and evenly consumed, preferably, before the pin contacts the now bare wire.
As the upper electrode continues to apply downward pressure, heat and current, the pin softens, but does not melt, and is compressed with the now uninsulated wire to form a reliable fusion compression joint.
Another exemplary embodiment includes an extended bottom electrode with a plurality of laterally spaced notches and grooves described above for receiving a plurality of wires and pins. With this embodiment, the operator can set up on a frame the entire pin/wire assembly for the multiplicity of joints. The upper or lower electrode is indexed and stepped relative to the frame so that the operator need only press the start key and the upper head will stop, compress, fuse and withdraw from in lateral sequence each of the plurality of wire/pin joints as described above. This embodiment greatly reduces the set up time and enhances the reliability of wire/pin joint and the uniformity and yield of the final product.
One embodiment of the multinotched lower electrode includes a transverse channel extending along the front and/or rear faces below the fusing notches and an opening defined through the electrode beneath each notch. These channels and/or openings function to concentrate the bottom electrode heat in the region below the notch bottom that is in contact with the wire to be joined.